Salt appetite results from sodium depletion in many species. Our findings show inhibition of salt appetite during infusions of carbachol (CBC) into the cerebral ventricles (IVT), even following severe depletion of sodium. Proposed studies will pursue this unusual relation between natriuresis and suppression of salt appetite. One series will provide an initial investigation of the behavioral and CNS effects of the atrial natriuretic peptides, atriopeptins. Rats will be infused IVT or iv with atriopeptins I and II under varying conditions of body hydration to assess changes in water intake, salt appetite, and urinary volume and chemistry. The studies will determine if the atriopeptins either inhibit or facilitate salt appetite. Other studies will explore the possible involvement of atriopeptins in the behavioral and natriuretic phenomena associated with IVT infusions of CBC, angiotensin II (AII), and hyperosmotic CSF by observing changes in the bioassayable content of the atrial peptides during prolonged infusions of these agents. A second major series will study the receptor mechanisms involved in suppression of salt appetite and stimulation of natriuresis during IVT infusions of CBC and hyperosmotic CSF. Blocking studies will employ antagonists of cholinergic and AII receptors in an effort to release salt appetite from inhibition, and to study the possible involvement of these receptors in the response to hyperosmotic conditions. Further studies will test the effects of iv replacement of sodium on the behavioral and renal responses to IVT infusions of CBC and hyperosmotic CSF, to determine if sodium depletion can account for the rapid decline in drinking and natriuresis during these infusions. These studies will contribute to the general understanding of central control mechanisms supporting these poorly understood phenomena, and provide useful information toward a behavioral technology of drugs with diuretic properties.